1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor device including at least one of processes containing a process for heat-treating an impurity region provided by implanting impurity ions into a semiconductor substrate and a process for activating a polycrystalline semiconductor layer deposited on an insulation film.
2. Description of the Related Art
When a semiconductor region of a predetermined conductivity type is formed in an epitaxial layer or a semiconductor substrate of single crystal by an ion-implantation technique, the epitaxial layer is subjected to damage, and the ion-implanted region becomes amorphous. For diffusing the implanted impurity into the epitaxial layer, a heat treatment is usually performed in a nitrogen gas atmosphere at about 1200.degree. C. for three hours. During this treatment, there occurs a damage recovery phenomenon wherein the amorphous region is restored to a single crystal state. However, inventors have found that since the heat treatment requires a high temperature and a long time, high density crystal defects are generated in the epitaxial layer or semiconductor substrate, depending upon unwanted nuclei caused by the damage due to the ion-implantation and by contamination in the manufacturing process. The crystal defects may decrease the breakdown voltage of semiconductor devices such as power MOSFETs (power MOS field effect transistors), or may increase an undesirable leakage current.
A polycrystalline semiconductor layer, such as a polysilicon layer provided on an insulation film, has been used as an electrode or an interconnection layer in various semiconductor devices including integrated circuits. Though, the polysilicon layer has been activated in a nitrogen atmosphere, the grain boundaries of the polysiicon layer are abnormally grown according to conditions of treating time and temperature. The abnormally-grown grain boundaries are very easily oxidized and, for example, they are easily oxidized in a thermal diffusion process. When the polysilicon layer having the oxidized grain boundaries is subjected to etching after the activation treatment, the grain boundaries are removed by an etchant and unwanted pin-holes are formed in the insulation film provided under the polysilicon layer. In a MOS semiconductor device, when the polysilicon layer is used as a gate electrode, pinholes are provided in an underlying gate oxide film, thereby bringing unwanted insulation deterioration between the gate electrode and the source or drain region.
At any rate, the problems described above may reduce the reliability and the yield of semiconductor devices.